How did The Romance of the Three Kingdoms form a great war in the Three Kingdoms?

Since it is said that it is Chibi, I will say that it is the battle of Yiling, because after Battle of Red Cliffs (1), there are still separatist forces such as Marten, Liu Zhang and Zhang Lu, not "three legs"; (2) Before the Yiling War, the power of Shu reached its peak. If Liu Bei listens to everyone's advice, saves his strength and joins hands with Wu to fight Cao, the general trend of the world will probably change. (3) After the battle of Yiling, Shu was badly weakened, which broke the balance of the alliance between Shu and Wu. Since then, Shu has no power to compete with Cao Wei, and Soochow can only protect itself. Wei couldn't swallow the two countries for a while, forming a "three-legged" trend.